A major US-designed polio vaccine was first tested in the Soviet Union

Jonas Salk developed the first successful polio vaccine—and tested it on himself

The American medical researcher developed the inactivated virus vaccine from 1952 to 1955 and proved that it could prevent disease. He tested the virus on himself and his family in 1954 and then carried out formal clinical trials on more than 1.3 million children.

Inactivated polio virus vaccine is the only one offered in the US—it contains no live virus

Inactivated polio virus vaccines cannot cause illness because the virus isn't alive. It's been the only polio inoculation offered in the United States since 2000 and provides almost complete protection

Oral polio vaccines cause approximately 250 to 500 polio cases per year globally

Live, weakened polioviruses in the oral vaccine can very rarely mutate into a disease-causing form and lead to vaccine-associated paralytic poliomyelitis. This oral vaccine is not available in the United States.

Live virus vaccines predated polio—that's how we vaccinate against smallpox

Since 1796, smallpox vaccines have used a live poxvirus related to smallpox. Yellow fever vaccines have used a live weakened form of the virus responsible for yellow fever since 1937.

The oral, live virus vaccine is the most robust but carries more risks

The live virus vaccine, delivered via oral drops, induces the best protection in the body. Because it includes a live, weakened form of the virus there's an extremely small risk it can sicken recipients and potentially cause paralysis. Recipients also shed the virus in their stool, which can rarely lead to vaccine-derived cases of the virus if the virus mutates. (Some users may experience a paywall.)

Most polio cases today are vaccine-derived rather than naturally occuring

Weakened, live virus vaccines—which aren't offered in the US—carry a risk of virus being shed in the stool. Rarely, the shed virus mutates and leads to vaccine-derived polio infections. Most recent polio cases are genetically linked to those vaccines. As shown in this graphic, there are typically hundreds of vaccine-derived polio cases annually.

A 1954 outbreak at a Boston boarding school allowed scientists to isolate the measles virus and formed the basis for the first measles vaccine.

Needle-free polio vaccines were offered in Afghanistan for the first time in 2026

Fear of needles has been one barrier to eradicating polio in Afghanistan. Vaccinators are now using a needle-free jet injector to deliver the vaccine through the skin—an approach that's previously been used in other locations. The inoculation includes the inactivated virus vaccine (the vaccine without any live virus in it).

Wastewater testing has detected genetic evidence of polio, triggering vaccine boosters

Sampling of wastewater in London in 2022 detected fragments of polio virus, suggesting a vaccine-derived version of polio may be circulating. No one became ill, but the finding did trigger calls for a renewed booster inoculation campaign.

Improved 19th-century sanitation meant kids encountered polio later, with worse results

Almost all children likely used to contract poliovirus, but scientists suggest that when infants encountered it very early in life—due to poorer conditions and hygiene—they still had some maternal protection from pregnancy or through breastmilk, so the symptoms were more flu-like.

Polio is currently circulating in only two countries but it remains difficult to eradicate

Wild polio virus is only endemic in two places. Afghanistan and Pakistan are the last two countries with naturally occurring polio cases. Vaccination campaigns have been plagued by misinformation, Taliban bans on vaccines, distrust of public health workers, and violence, including the killing of vaccinators.

The COVID-19 pandemic led to a decrease in immunizations in the US and worldwide

Public health funds and resources that were diverted to COVID-19 response reduced efforts to combat polio and vaccinations for polio and other diseases declined during the pandemic, putting more people at risk for polio.

Polio commonly spreads when virus-laden feces gets into our mouths

This highly infectious disease is transmitted from one person to another, mainly when we eat virus-laden poop particles. Less frequently, contaminated food or water can transmit the virus, or people can be infected via respiratory droplets (from coughing or sneezing).

The Soviet Union’s surprising first atomic test ended the US nuclear monopoly

In 1949, the USSR successfully tested its first atomic bomb—ending the US monopoly on nuclear weapons and sparking an arms race that would define the Cold War.

The US military, concerned about potential deployments worldwide, has long funded experimental hantavirus vaccines and therapies.

Collaborations between the military, biotech, and academic researchers led to an experimental antibody treatment for the Andes hantavirus strain—the one that more readily passes between humans. As of spring 2026, it had only been tested in animals. The US Army has also tested a potential hantavirus vaccine in people. It published early findings in 2023 that seemed promising, eliciting some immune system response. (Some users may encounter a paywall.)

Before vaccines, there was 'variolation': what was it?

Before the technology behind vaccinations was discovered, some keen observers of medicine around the globe noticed how previous infections could impact future ones. Learn about the techniques early physicians used before they had vaccines.

See when the last case of wild poliovirus was found in each country

This chart shows when wild polio cases were last reported in each country worldwide. Beyond wild poliovirus, rare outbreaks can occur related to mutated strains of oral polio vaccine.

A scientist successfully treated her own breast cancer by injecting the tumor with lab-grown viruses.

Only one strain of wild poliovirus continues to infect humans

Three strains of polio used to regularly infect humans, but two of the strains were declared eradicated in 2015 and 2019, respectively. In 2019, world health leaders estimated complete polio eradication—if achieved—would save $14B by 2050.

'Our greatest responsibility is to be good ancestors.'

- Polio vaccine developer Jonas Salk (1914–1995)

During the Cold War, the Soviet Union created a Eurovision competitor

The Soviet Union was not a member of the European Broadcasting Union, so it couldn't compete in Eurovision. In 1977, it turned a preexisting Polish-language singing competition into one that more closely resembled Eurovision and renamed it Intervision. The competition was open to countries from across the globe, regardless of their form of government, though most entrants were from communist countries.

The flu vaccine has evolved alongside discoveries of new virus strains

After influenza B was identified in 1940, researchers created a two-strain vaccine by 1942. The WHO later built a global surveillance system to track mutations, enabling vaccines to be updated annually to target the strains most likely to circulate.

Spies working on the Manhattan Project propelled the Soviet bomb program

Soviet infiltration—most notably by Klaus Fuchs—smuggled detailed implosion-design and hydrogen‑bomb data from Los Alamos to Moscow, cutting the USSR’s development time by at least a year and enabling their first atomic test in August 1949.

View this timeline of polio milestones and vaccine development

Polio has a long history in art and medicine, dating back centuries. It includes a representation of an apparent polio survivor with a shriveled leg in ancient Egyptian art. See milestones in the history of polio in this timeline.

Sputnik 1—launched in 1957—was Earth's first artificial satellite

Its launch accelerated US investment in the Space Race amid fears the Soviet Union had the technology to launch intercontinental nuclear warheads. It would be followed by Sputnik 2, which carried the first living being—a dog named Laika—to orbit.

The USSR launched the world's first satellite, Sputnik 1, into space in 1957

Sputnik, launched by the Soviet Union in 1957, became the world's first artificial satellite. While the technology itself was limited, the launch ignited the space race and signaled that intercontinental missiles and space technology had arrived faster than American leaders expected.

A fake vaccine campaign was used to locate Osama bin Laden, fueling vaccine distrust

As part of the intelligence operation to find bin Laden in Pakistan, the US Central Intelligence Agency recruited a Pakistani doctor who ran a fake hepatitis B vaccine campaign and obtained DNA samples from bin Laden. News of this fake campaign fueled further distrust of healthcare workers, attacks on them, and stymied efforts to vaccinate against polio in the region.

Sparkling wine was a political tool in the Soviet Union

To show the world that the Soviet Union had recovered after the devastating famine of the early 1930s, leader Josef Stalin turned to a surprising source: sparkling wine. Stalin believed that if everyday citizens could access luxury goods like caviar and Champagne, it would show socialism had succeeded. The result was Sovetskoye Shampanskoye, a Soviet-made sparkler that achieved his goal of availability and affordability if not quality.

Humans are the only known reservoir of poliovirus

The virus has not been found in any other species, which makes humans the only known reservoir for polio. In laboratory settings, nonhuman primates have also been infected with the virus, but there's no evidence that they contract the virus in nature.

What are universal vaccines?

As viruses mutate and develop, vaccines have to adapt, leading to regular recommended injections like flu shots. Researchers are working to develop universal vaccines that aim to protect against multiple virus variants if not entire virus families. These vaccines work by creating broadly neutralizing antibodies (bnAbs) that target aspects of viruses that don't typically mutate and are integral to the virus' survival.

Two Lyme disease vaccines were in development in 2026

As of early 2026, there was no vaccine for Lyme disease available. One candidate vaccine, VLA15, was in later-stage clinical trials. Another designed to provide seasonal protection was licensed to a pharmaceutical company in 2025, and was planned for human clinical trials.

The iron lung—a simple mechanical ventilator—was first used to treat polio

These breathing devices, developed in the late 1920s at Harvard, were used to treat polio patients with breathing difficulties. Watch this video describing how these negative pressure devices work.

Variola: the second-deadliest virus on Earth

Because it was declared eradicated in 1980, many forget smallpox is one of history's deadliest diseases—in its final century, it's estimated to have claimed 500 million lives. This 11-minute video from production studio Kurzgesagt takes a look at...

In 1933, the influenza virus was first identified through 'ferret flu' experiments, which proved that the disease was viral—not bacterial.

Propaganda became a key weapon in the US–Soviet Cold War

Both superpowers waged a global battle for hearts and minds through propaganda—using film, radio, art and education to promote their values. The US emphasized freedom and prosperity, while the USSR championed socialism and anti-imperialism.

See the polio cases that occur worldwide each year by region

Worldwide, the number of cases of polio reported each year from 1980 to 2024 has declined. This graphic depicts regional trends and declines by year.

Attenuated vaccines introduce a weakened version of the virus into the body

Some vaccines, like those for measles, rely on weakened versions of a virus. These weakened pathogens are introduced into the body, triggering an immune response and helping the immune system learn to protect itself against stronger versions of the virus. (This also explains why some vaccines make you feel under the weather.)

Measles infection, which was nearly universal during childhood in prevaccine era, was described by the Persian physician Rhazes in the 10th century as "more to be dreaded than smallpox."

The US and the USSR each boycotted Olympic Games during the Cold War

The US led a boycott of the 1980 Moscow Olympics over the Soviet invasion of Afghanistan. In retaliation, the USSR and its allies skipped the 1984 Los Angeles Games.

Learn how the Soviets won the early space race

This video traces how Cold War arms competition transformed rocketry into a symbol of global power, following pioneers like Tsiolkovsky and von Braun through World War II and into the 1950s, culminating in the Soviet Union’s launch of Sputnik I in 1957.

The measles vaccine has saved an estimated 94 million lives since its introduction.

An Ebola vaccine was developed during the 2018 west African Ebola outbreak, but the 2026 Ebola outbreak is with a different species of the virus, not the one that the vaccine is approved to treat.

The 2026 Ebola outbreak in the DRC is spurring new Ebola vaccine development for the Bundibugyo species.

The USSR's space program achieved many historic firsts in the Space Race

Soviet scientists launched the first satellite, sent the first human into orbit, and carried out early spacewalks—milestones that gave the USSR a decisive early lead in the Space Race and reshaped global competition in science and technology.

Using mosquitoes to vaccinate bats could curb the spread of deadly diseases.

See the evolution of Ebola vaccine and treatment development.

How the 1918 pandemic spurred developments in virology and vaccines

This article provides an in-depth historical account of the 1918 Spanish Flu pandemic, including its impact on the global population and how its occurrence spurred significant advancements in the study of viruses—laying the groundwork for the...

Approximately 70% of all polio infections in children are asymptomatic

Most polio infections are asymptomatic or appear with only flu-like symptoms. Infected individuals can still shed the virus in their stool and mucus for days or weeks

Watch a 1957 news report on the Sputnik launch

This 1957 news report captures the shock and uncertainty that followed the launch of Sputnik, showing how the first artificial satellite immediately altered global politics, military planning, and public perceptions of technological power.

Most flu vaccines are still produced using chicken eggs

For decades, influenza vaccines have been made by growing viruses inside fertilized chicken eggs. Though newer methods using cell cultures or recombinant technology exist, egg-based production remains the primary global manufacturing process.